Copolymer blend compositions for use to increase paper filler content

ABSTRACT

Methods for making a heterogeneous polymer blend comprising one or more anionic polymers, one or more cationic polymers, and one or more non-ionic polymers, which method comprises (a) adding to a non-neutral solution a first amount of polymerization initiator and one or more anionic or cationic monomers, wherein each monomer has the same charge; (b) a second amount of the polymerization initiator and one or more non-ionic monomers; (c) adding a third amount of the polymerization initiator and one or more ionic monomers that are oppositely charged from the monomers of (a); adding stepwise, a fourth amount of the polymerization initiator to react any residual monomer, and (e) neutralizing the resulting polymer blend. Also claimed are heterogeneous polymer blends containing polymers formed from one or more anionic, cationic, and non-ionic monomers, either polymerized in situ or separately and then combined.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. application Ser. No.12/562,446, filed Sep. 18, 2009 and U.S. Provisional Application No.61/192,891, filed Sep. 22, 2008, the entire contents of each are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

In the papermaking industry, substituting inorganic filler for woodfiber in paper and paperboard is advantageous because the inorganicfiller is generally less expensive than wood fiber and the substitutionlowers costs. Precipitated calcium carbonate is commonly used as afiller in the industry, Although inorganic fillers decrease the totalcost of papermaking, increasing concentrations can reduce the overallbulk, strength, and stiffness of the paper—all of which are importantend use performance properties.

In this decrease in strength and stiffness in the final paper product isa result of the structure of the wood pulp and inorganic filler. Duringthe papermaking process, the long wood pulp fibers become entangled,thus creating a strong web of fiber. The inorganic filler does not havethese long fiber chains, so increasing the inorganic filler content canweaken the fiber web in the finished product. In addition, as theinorganic filler content increases, the never-dried strength of the wetweb exiting the press section of a paper machine decreases. Thisstrength decrease affects machine runnability and may force the papermachine to run at lower yields because of a lower thru-pat or higherdowntime because of web breaks in the wet web.

Although the prior art teaches treatments, as part of the papermakingprocess, for increasing the retention of fine inorganic fillers in thefinal paper or paperboard product, the prior art does not disclosemethods to increase the inorganic filler content of paper whilesimultaneously maintaining the weight, strength, and runnability of theend product.

For example, dry strength resins are known in the prior art and canincrease the strength of the finished paper product When mixed into theinitial paper pulp slurry (also called a paper furnish). Amphoteric,water-soluble dry strength resins are known in the prior art. Amphotericresins are typically made by reacting acrylamide with cationic andanionic monomers (for example, diallyldimethylammonium chloride(“DADMAC”) and acrylic acid) in a free radical copolymerizationreaction. These resins are generally limited to 10-15 mol % of eachionic component (20-30 mol % charged polymer total). If the ionicpolymer concentration is higher, the solution becomes unstable.

Additionally, separate anionic and cationic polymeric dry strengthresins are also known in the prior art. Typically, these resins will beadded sequentially—i.e. all the resin of one charge is added, then allthe resin of the opposite charge is added. When anionic and cationicresins are added as separate resins, the anionic resin is typically anacrylamide/acrylic acid copolymer. The cationic typically containseither DADMAC, acryloylethyltrimethylammonium chloride (“AETAC”), or ahydrolyzed form of vinyformamide.

For example, the inorganic filler content of paper may he increased bytreating the pulp slurry and inorganic filler separately with a chargedpolymer, then treating the filler with an oppositely charged ionic, andmixing the treated filler and pulp slurry together. Alternatively, onemay treat only the inorganic filler with a charged polymer, and thencombine the treated filler with the pulp slurry for processing intopaper.

Another method to maintain paper bulk as the inorganic filler content ofpaper is increased is to increase the average inorganic filler particlesize. An increase in filler concentration and/or filler particle sizecan lead to additional abrasion on the paper slurry processing surfaces.This abrasiveness generally manifests itself as additional wear on thewet end of the paper making process, especially on the paper formingfabrics and static drainage elements. Additionally, the increased wearon these parts, slitter knives, and other surfaces may degrade thequality of the final paper product and increase maintenance andservicing costs for the equipment. Previous attempts to mitigate theseproblems have included addition of surfactants and TEFLON(polytetrafluoroethylene) to the paper slurry.

BRIEF SUMMARY OF THE INVENTION

The invention relates, in general, to the surprising discovery thatheterogeneous polymer blends that contain polymers composed of at leastone anionic, one cationic, and one nonionic monomer may be used toincrease the inorganic filler content of paper without negativelyaffecting paper strength, weight, or runnability. This discovery allowsfor the cost-effective production of paper or paperboard. The presentinvention also relates in one aspect to a novel method of creating thenovel heterogeneous polymer blends. Finally, the present invention alsorelates in another aspect to methods of using the heterogeneous polymerblends with a precipitated calcium carbonate filler to maintain thestrength, weight, and runnability of paper or paperboard.

One embodiment of the present invention is a method of making aheterogeneous polymer blend for increasing the inorganic filler contentof paper or paperboard, comprising: (a) adding to a non-neutral solutiona first amount of polymerization initiator and one or more anionic orcationic monomers, wherein each monomer has the same charge; (b) addinga second amount of the polymerization initiator and one or morenon-ionic monomers to the solution; (c) adding a third amount of thepolymerization initiator and one or more ionic monomers that areoppositely charged from the monomers of step (a); and (d) adding,stepwise, a fourth amount of the polymerization initiator to react anyresidual monomer and resulting in the heterogeneous polymer blend, and(e) if necessary, neutralizing the resulting heterogeneous polymerblend, wherein the polymerization initiator is selected from the groupconsisting of water soluble azo initiators.

The anionic monomer(s) may be: (1) acrylic acid, (2) methacrylic acid,(3) styrenesulfonic acid, (4) vinylsulfonic acid, (5)acrylamidomethylpropane sulfonic acid, or (6) mixtures thereof.

The cationic monomer(s) may be: (1) diallyldimethylammonium chloride,(2) acryloylethyltrimethyl ammonium chloride, (3) methacryloylethyltrimethyl ammonium chloride, (4) acryloylethyltrimethylammonium sulfate.(5) methacryloylethyl trimethyl ammonium sulfate, (6)acrylamidopropyltrimethyl ammonium chloride, (7) methacrylamidopropyltrimethyl ammonium chloride, (8) non-quaternized forms of (2)-(7), (9)vinylformamide (subsequently hydrolyzed to vinylamine), or (10) mixturesthereof.

The nonionic monomer(s) may be: (1) acrylamide, (2) methacrylamide, (3)N-alkylacrylamide, (4) vinylformamide, or (5) mixtures thereof.

Another embodiment of the invention is a heterogeneous polymer blendcomprising: (a) one or more anionic polymers formed from monomersselected from the group: (1) acrylic acid, (2) methacrylic acid, (3)styrenesulfonic acid, (4) vinylsulfonic acid, (5)acrylamidomethylpropane sulfonic acid, and (6) mixtures thereof; (b) oneor more cationic polymers formed from monomers selected from the group:(1) diallyldimethylammonium chloride, (2) acryloylethyltrimethylammonium chloride (3) methacryloylethyl trimethyl ammonium chloride, (4)acryloylethyltrimethylammonium sulfate (5) methacryloylethyl trimethylammonium sulfate, (6) acrylamidopropyltrimethyl ammonium chloride, (7)methacrylamidopropyl trimethyl ammonium chloride, (8) non-quaternizedforms of (2)-(7), (9) vinylformamide (subsequently hydrolyzed tovinylamine), and (10) mixtures thereof; (c) one or more non-ionicpolymers formed from monomers selected from the group: (1) acrylamide,(2) methacrylamide, (3) N-alkylacrylamide, (4) vinylformamide, and (5)mixtures thereof;

The heterogeneous polymer blend may also contain (a) one or morecopolymers comprising at least one anionic monomer and at least onenon-ionic monomer; (b) one or more copolymers comprising at least onecationic monomer and at least one non-ionic monomer.

The heterogeneous polymer blend may also contain one or more terpolymerscomprising at least one anionic monomer, at least one cationic monomer,and at least one non-ionic monomer.

Yet another embodiment of the invention is a method of increasing thefiller content of a sheet of paper or paperboard comprising: (a)combining the heterogeneous polymer blend with a precipitated calciumcarbonate filler to form a mixture; (b) combining the resulting mixturewith a pulp slurry; and (c) processing the resulting pulp slurry mixtureto form a sheet of paper or paperboard.

Another embodiment of the invention is a method of increasing the fillercontent of a sheet of paper or paperboard comprising: (a) combiningeither the heterogeneous polymer blend or a precipitated calciumcarbonate filler with a pulp slurry to form a mixture; (b) combining theremaining component from step (a) with the pulp slurry mixture; and (c)processing the resulting pulp slurry mixture to form a sheet of paper orpaperboard.

Another embodiment of the invention is a method of increasing the fillercontent of a sheet of paper or paperboard comprising: (a) combining apoly-diallyldimethylammonium chloride/acrylamide/acrylate copolymermixture with a precipitated calcium carbonate filler; (b) combining theresulting mixture with a pulp slurry; and (c) processing the resultingpulp slurry to form a sheet of paper or paperboard.

Yet another embodiment of the invention is a method of increasing thefiller content of a sheet of paper or paperboard comprising: (a)combining either a poly-diallyldimethylammoniumchloride/acrylamide/acrylate copolymer mixture or a precipitated calciumcarbonate filler with a pulp slurry; (b) combining the remainingcomponent from step (a) with the pulp slurry mixture; and (c) processingthe resulting pulp slurry mixture to form a sheet of paper orpaperboard.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the singular terms “a” and “the” are synonymous and usedinterchangeably with “one or more” or “at least one” unless the contextclearly indicates a contrary meaning. Accordingly, for example, areference to “a compound” herein, or in the appended claims, can referto a single compound or more than one compound. Additionally, allnumerical values, unless otherwise specifically noted, are understood tobe modified by the word “about.” For all the compositions and processesincluded herein, it should be understood that there will be at leasttrace amounts of the unreacted constituent components, including anymonomers and polymer reaction initiators used. Unless otherwiseindicated “weight %” refers to the weight of the solids in a particularblend and excludes the weight of the water contained in the aqueoussolution.

Compositions and processes in accordance with the various embodiments ofthe present invention are suitable for use to increase the inorganicfiller content of paper and paper hoard. The present invention alsoincreases the runnability of wet web paper furnish. The presentinvention includes a novel heterogeneous polymer blend of polymersformed from anionic, cationic, and nonionic monomers. The presentinvention also includes an in-situ method of making the novelheterogeneous polymer blend. Also included in the present invention is amethod of increasing the inorganic filler content of paper or paperboardby treating the pulp slurry with the heterogeneous polymer blend and aprecipitated calcium carbonate filler. Finally, included in the presentinvention is a method of increasing the inorganic filler content ofpaper by treating a pulp slurry with a poly-diallyldimethylammoniumchloride/acrylamide/acrylate copolymer mixture and a precipitatedcalcium carbonate filler.

Stable, aqueous heterogeneous polymer blend compositions can be preparedin-situ via a stepwise reaction method in a non-neutral solution. Priorto, and during, the reaction, the solution is non-neutral to minimizethe reaction between the anionic and cationic monomers. The methodcomprises the steps of (a) polymerizing one or more anionic monomersusing a thermal polymerization initiator in anon-neutral solution; (b)adding one or more nonionic monomers and additional thermalpolymerization initiator to the solution; (c) adding one or morecationic monomers and additional thermal polymerization initiator to thesolution; (d) reacting any residual monomer with additional thermalpolymerization initiator; and (e) neutralizing the resulting aqueousheterogeneous polymer blend. The resulting heterogeneous polymercomposition contains, at most, nonionic homopolymer, cationichomopolymer, anionic homopolymer, anionic/nonionic copolymer,cationic/nonionic copolymer, and, optionally, anionic/nonionic/cationicterpolymer. It is understood in the art that the above composition willcontain trace amounts of both the thermal polymerization initiator andthe constituent monomer components.

As illustrated in the Examples set out below, the addition order of themonomer components may be reversed, so that the cationic monomer isreacted first and the anionic monomer is reacted last. Alternatively,heterogeneous polymer blends may be formed by polymerizing the anionic,cationic, and nonionic monomers separately, and then combining theresulting polymers into a blend. Preferably, the heterogeneous polymerblends are created via in-situ reaction.

The polymerization initiator may be any known polymerization initiationtechnique, including, but not limited to oxidative reduction and thermalpolymerization. Preferably, the polymerization initiator is a thermalpolymerization initiator. More preferably, the polymerization initiatoris a water-soluble azo initiator. Most preferably, the polymerizationinitiator is azodiisobutyramidine dihydrochloride (V50), available fromWako, Richmond, Va.

The monomers may be any monomers widely used in the papermakingindustry. Preferably, the anionic monomer is acrylic acid, methacrylicacid, styrenesulfonic acid, vinylsulfonic acid, oracrylamidomethylpropane sulfonic acid. More preferably, the anionicmonomer is acrylic acid.

Preferably, the cationic monomer is diallyldimethylammonium chloride;acryloylethyltrimethyl ammonium chloride; methacryloylethyltrimethylammonium chloride; acryloylethyltrimethylammonium sulfate;methacryloylethyl trimethyl ammonium sulfate; acrylamidopropyltrimethylammonium chloride; methacrylamidopropyl trimethyl ammonium chloride; thenon-quaternized forms of acryloylethyltrimethyl ammonium chloride,methacryloylethyl trimethyl ammonium chloride,acryloylethyltrimethylammonium sulfate, methacryloylethyl trimethylammonium sulfate, acrylamidopropyltrimethyl ammonium chloride,methacrylamidopropyl trimethyl ammonium chloride; and vinylformamide(subsequently hydrolyzed to vinylamine). More preferably, the cationicmonomer is diallyldimethylammonium chloride.

Preferably, the nonionic monomer is acrylamide, methacrylamide,N-alkylacrylamide, or vinylformamide. More preferably, the nonionicmonomer is acrylamide.

The molar ratio of each component of the heterogeneous polymer blend mayrange from about 1 mol % to about 50 mol % of each monomer. Preferably,the molar reactant ratio is in the range of from about 10 to about 30mol % anionic monomer, from about 40 to about 80 mol % nonionic monomer,and from about 10 to about 30 mol % cationic monomer.

Depending on the molar ratio of each monomer component present, thefinal heterogeneous polymer blend may carry a positive or negativecharge, or may be essentially isoelectric. Preferably, the molar ratiosof the anionic and cationic components are selected such that theheterogeneous polymer blend is essentially isoelectric at a neutral pH.There may be, however, applications where a net anionic or cationiccharge is advantageous.

Monomers polymerize linearly unless in the presence of bi-functionalcompounds. If branched polymers are necessary for a particularapplication, small concentrations of bi- or multi- functionalcompound(s) may be added to one or more steps of the polymerizationreaction. Preferably, the reaction does not contain bi- ormulti-functional compounds and the resulting polymers are substantiallylinear.

The heterogeneous polymer blend may be used in any form conventionallyused in the papermaking industry, including, but not limited to, aqueoussuspensions; inverse emulsions and microemulsions; brine dispersions;and dried or precipitated polymer blends that have been ground orpowdered. Preferably, the heterogeneous polymer blend is used in astable aqueous suspension.

The heterogeneous polymer blends may be used to substantially increasethe inorganic filler content of paper or paperboard while maintainingthe physical properties including bulk (weight), runnability, andstrength of the resulting product. The increased filler content isadvantageous in papermaking because inorganic filler is inexpensiverelative to virgin or recycled wood fiber.

The heterogeneous polymer blends can increase the inorganic fillercontent of paper or paperboard by 10% (based on dry weight) withoutlowering other physical properties of the final paper product. Thepresent invention may be used with any inorganic filler, including, butnot limited to, precipitated calcium carbonate, ground calciumcarbonate, kaolin clay, calcined kaolin clay, talc, calcium sulphate,calcium phosphate, and titanium dioxide. Preferably, the inorganicfiller is precipitated calcium carbonate, ground calcium carbonate, orkaolin clay. More preferably, the inorganic filler is precipitatedcalcium carbonate. Most preferably, the inorganic filler isacicular-aragonite precipitated calcium carbonate or clusteredscalenohedral calcite precipitated calcium carbonate. The preferredembodiments of the present invention provided higher finished sheetstiffness levels than other inorganic fillers.

The heterogeneous polymer blends of the present invention may be mixedwith the inorganic filler as a filler pre-treatment before final mixturewith the pulp slurry or the heterogeneous polymer blends and theinorganic fillers may be added stepwise to the pulp slurry. Preferably,the heterogeneous polymer blend and the inorganic filler are mixedbefore addition to the pulp slurry. The compounds of the presentinvention may also be applied in the wet end, of the paper machine.

The heterogeneous polymer blend is effective for a wide range oftreatment levels. Preferably, the pulp slurry is treated with from about0.05 to about 1 wt % of the heterogeneous polymer blend relative to thetotal dry weight of the papermaking furnish (pulp slurry plusadditives). More preferably, the pulp slurry is treated with from about0.1 to about 0.5 wt % of the heterogeneous polymer blend relative to thetotal dry weight of the papermaking furnish.

The heterogeneous polymer blends may be used in a wide range of finalpaper products and paper grades, including, but not limited to, uncoatedcopy paper, coated fine paper, coated mechanical paper, uncoatedmechanical paper, and packaging paper.

In addition to maintaining desirable finished paper qualities whileincreasing the amount of total inorganic filler in the finished paper orpaperboard, the present invention has the unexpected benefits ofincreasing the runnability of pulp slurries with high filler content andproviding lubrication for the forming fabrics and stationary dewateringelements of the paper machine. The polymeric blends increase thecohesion of never-dried wet webs containing high filler loadings; thiscohesion improves the machine runnability at high filler loadings.Additionally, as the inorganic filler content of pulp slurry increases,the mechanical parts of the paper machine face greater abrasion from theinorganic filler. This abrasion increases maintenance costs and machinedowntime, thus reducing productivity. Increased fabric and parts lifecan reduce the overall cost of paper production and increase machineon-stream time.

Slip agents, such as TEFLON, can be used to decrease the frictionexperienced by the paper machine, but these agents may have negativeimpacts on finished paper product quality and are often expensive. Theheterogeneous polymer blend of the present invention unproved fabriclife on paper machines under laboratory tests. Treatment of the pulpslurry with the compound of the present invention will reduce abrasionwith treatment levels from about 0.01 to about 10 wt % based on thetotal dry weight of the filler. A dosage of about 1.5 wt % based on thetotal dry weight of the filler is preferred. The heterogeneous polymerblend may be applied to reduce abrasion in the same manner as toincrease the inorganic filler content of the finished paper orpaperboard.

EXAMPLES

The following Examples help to illustrate embodiments of the presentinvention.

For each of the following examples, weight % refers to the weight % ofthe active polymer solids and excludes the aqueous solution. ForExamples 7-14, which describe methods of using the novel heterogeneouspolymer blend to increase the filler content of pulp slurry, all productdosages are expressed as active (solids) material as a percentage of thetotal dry material being treated (wood fiber plus filler and otheradditives); water is excluded from the calculation.

Example 1 Synthesis of an In-Situ Heterogeneous Polymer Blend

Samples of the heterogeneous polymer blend were prepared by thefollowing method. Acrylamide, available from SNF, Riceboro, Ga., andDADMAC, available from Kemira, Kennesaw, Ga., were placed in separateflasks and sparged with oxygen-free nitrogen for thirty (30) minutes,1.10 grams of 10% Copper (II) Sulfate, available from Sigma Aldrich, St.Louis, Mo., was added to the flask containing the sparged acrylamidesolution and the flask was monitored to avoid a runaway exothermicreaction.

Separately, a 3,000 mL 4-neck round bottom flask was equipped with acondenser, a mechanical stirrer, a thermocouple attached to a regulator,a nitrogen inlet for sparging, a nitrogen outlet, and a heating mantle.35.51 g acrylic acid, available from Rohm & Haas, Philadelphia, Pa., wasadded to the flask. The flask was charged with 1432.53 g of deionizedwater and sparged with oxygen-free nitrogen for thirty (30) minutes.

In a separate 100 mL round bottom flask, 46.87 g of 10% solution ofa,a′-azodiisobutyramidine dihydrochloride (V50), available from Wako,Richmond, Va., was added and stirred at 275 RPM while sparging withoxygen-free nitrogen for thirty (30) minutes. Twenty percent (20%) (9.37g) of the sparged V50 was added to the acrylic acid. The 3000 mL flaskwas heated to 55° C. for thirty (30) minutes while stirring at 275 RPM.The temperature was monitored to ensure that there was not a runawayexothermic reaction. An ice bath was kept available to control thetemperature.

323.63 g of the sparged acrylamide solution was added to the 3000 mLflask, then an additional 20% (9.37 g) of the sparged V50 was added. The3000 mL flask was heated to 55° C. for thirty (30) minutes whilestirring at 275 RPM. After thirty (30) minutes, the temperature wasadjusted to 65° C. and 121.33 g of the sparged DADMAC solution wasadded. A syringe pump was charged with the remaining V50 solution (28.12g). Forty percent (40%) of the V50 solution (11.25 g) was addeddrop-wise over the next 270 minutes while heating and stirring thesolution at 275 RPM.

After 270 minutes, the temperature of the 3000 mL flask was increased to75° C. and the remaining V50 solution (16.87 g) was added drop-wise overthe next thirty (30) minutes. After thirty (30) minutes, the temperatureof the 3000 mL,: flask was increased to 80° C. and heated at 80° C. foran additional sixty (60) minutes. The resulting solution was cooled toroom temperature. The pH of the solution was measured and adjusted to 7using sodium hydroxide.

The reaction resulted in a stable, opaque suspension of a heterogeneouspolymer blend containing polyacrylamide, sodium polyacrylate,poly-acrylamide/acrylate copolymer, poly-DADMAC, poly-DADMAC/acrylamidecopolymer, and a poly-acrylamide/acrylate/DADMAC terpolymer with anactive polymer concentration of 10% and a Brookfield viscosity of 3000cps (measured using a #3 LVT spindle, 30 RPM at 22° C.). The blendfractions were calculated using kinetic sampling and 1H NMR sampling ofthe in-process composition. The product was also analyzed post-reactionusing 13C NMR. The final heterogeneous polymer blend contained thefollowing (as a weight percent of the polymer solids): 13% polyacrylate,4% poly-acrylamide/acrylate copolymer, 64% polyacrylamide, 6%poly-DADMAC/acrylamide copolymer, 12% poly-DADMAC, and 1%poly-acrylate/acrylamide/DADMAC terpolymer. The heterogeneous polymerblend did not precipitate, gel, or separate when stored at roomtemperature for thirty (30) days.

Example 2 Synthesis of an In-Situ Heterogeneous Polymer Blend

Samples of the heterogeneous polymer blend were prepared by thefollowing method. Acrylamide, available from Kernira, Kennesaw, Ga., andDADMAC, available from Sigma Aldrich, St. Louis, Mo., were placed inseparate flasks and sparged with oxygen-free nitrogen for thirty (30)minutes.

Separately, a 500 mL 4-neck round bottom flask was equipped with acondenser, a mechanical stirrer, a thermocouple attached to a regulator,a nitrogen inlet for sparging, a nitrogen outlet, and a heating mantle14.06 g acrylic acid, available from Sigma Aldrich, St. Louis, Mo., wasadded to the flask. The flask was charged with 205 g of deionized waterand sparged with oxygen-free nitrogen for thirty (30) minutes. 0.24 g ofisopropanol, available from VWR, West Chester, Pa., was added to the 500mL flask.

In a separate 50 mL round bottom flask, 11.13 g of 20% solution ofa,a′-azodiisobutyramidine dihydrochloride (V50), available from Wako,Richmond, Va., was added and stirred at 275 RPM while sparging withoxygen-free nitrogen for thirty (30) minutes. Twenty percent (20%) (2.23g) of the sparged V50 was added to the acrylic acid. The 500 mL flaskwas heated to 45° C. for 45 minutes while stirring at 275 RPM. Thetemperature was monitored to ensure that there was not a runawayexothermic reaction. An ice bath was available to control thetemperature.

54.92 g of the sparged acrylamide solution was added to the 500 mLflask, followed quickly by 40% (4.46 g) of the sparged V50. The 500 mLflask was heated to 45° C. for 45 minutes while stirring at 275 RPM.After 45 minutes, 48.04 g of the sparged DADMAC solution and 20% (2.23g) of the sparged V50 were added. The 500 mL flask was heated at 45° C.for 45 minutes while stirring at 275 RPM.

After 45 minutes, the temperature of the 500 mL flask was increased to75° C. and the remaining V50 solution (2.23 g) was added. The mixturewas heated at 75° C. for one (1) hour. The resulting solution was cooledto room temperature. The pH of the solution was measured and adjusted to7 using sodium hydroxide.

The reaction resulted in a stable, opaque suspension of a heterogeneouspolymer blend containing polyacrylamide, sodium polyacrylate,poly-acrylamide/acrylate copolymer, poly-DADMAC, poly-DADMAC/acrylamidecopolymer, and a poly-acrylamide/acrylate/DADMAC terpolymer with anactive polymer concentration of 10.2% and a Brookfield viscosity of 580cps (measured using a #3 LVT spindle, 30 RPM at 22° C.). The blendfractions were calculated using kinetic sampling and 1H NMR sampling ofthe in-process composition. The heterogeneous polymer blend did notprecipitate, gel, or separate when stored at room temperature for thirty(30) days.

Example 3 Synthesis of an In-Situ Heterogeneous Polymer Blend

Samples of the heterogeneous polymer blend were prepared by thefollowing method. Acrylamide and DADMAC, both available from SNF,Riceboro, Ga., were placed in separate flasks and sparged withoxygen-free nitrogen for thirty (30) minutes.

Separately, a 500 mL 4-neck round bottom flask was equipped with acondenser, a mechanical stirrer, a thermocouple attached to a regulator,a nitrogen inlet for sparging, a nitrogen outlet, and a heating mantle.14.06 g acrylic acid, available from SNF, Riceboro, Ga., and 205.49 gdeionized water were added to the flask and stirred at 275 RPM for 30minutes while sparging with oxygen-free nitrogen.

In a separate 50 mL round bottom flask, 11.13 g of 20% solution ofa,a′-azodiisobutyramidine dihydrochloride (V50), available from Wako,Richmond, Va., was added and stirred at 275 RPM while sparging withoxygen-free nitrogen for thirty (30) minutes. Twenty percent (20%) (2.23g) of the sparged V50 was added to the acrylic acid. The 500 mL flaskwas heated to 45° C. for 45 minutes while stirring at 275 RPM. Thetemperature was monitored to ensure that there was not a runawayexothermic reaction.

54.92 g of the sparged acrylamide solution was added to the 500 mLflask, followed quickly by 40% (4.46 g) of the sparged V50. The 500 mLflask was heated to 45° C. for 45 minutes while stirring at 275 RPM.After 45 minutes, 48.04 g of the sparged DADMAC solution and 20% (2.23g) of the sparged V50 were added. The 500 mL flask was heated at 45° C.for 45 minutes while stirring at 275 RPM.

After 45 minutes, the temperature of the 500 mL flask was increased to75° C. and the remaining V50 solution (2.23 g) was added. The mixturewas heated at 75° C. for one (1) hour. The resulting solution was cooledto room temperature. The pH of the solution was measured and adjusted to7 using sodium hydroxide.

The reaction resulted in a stable, opaque suspension of a heterogeneouspolymer blend containing polyacrylamide, sodium polyacrylate,poly-acrylamide/acrylate copolymer, poly-DADMAC, poly-DADMAC/acrylamidecopolymer, and a poly-acrylamide/acrylate/DADMAC terpolymer with anactive polymer concentration of 10.4% and a Brookfield viscosity of 774cps (measured using a #3 LVT spindle, 30 RPM at 22° C.). The blendfractions were calculated using kinetic sampling and 1H NMR sampling ofthe in-process composition. The heterogeneous polymer blend did notprecipitate, gel, or separate when stored at room temperature for thirty(30) days.

Example 4 Synthesis of a Post-Reaction Polymer Blend

A heterogeneous polymer blend was synthesized using post reactionpolymers. First the three polymers were made. To make thepolyacrylamide, 219.9 g of acrylamide, available from SNF, Riceboro,Ga., was added to a 2000 mL round bottom flask and diluted with 800 g ofdeionized water. The mixture was stirred at 275 RPM and sparged withoxygen-free nitrogen for thirty (30) minutes. After thirty (30) minutes,0.11 g of Copper (II) Sulfate was added. The reactor was heated to 45°C. and 35.6 g of a 10% V50 solution in deionized water was added to theflask. The reaction exothermed to 50° C. and exhibited high viscosity.To reduce viscosity, 400 g of deoxygenated, deionized water was added.After 45 minutes, 17.8 g of 10% V50 solution was added to the flask andthe flask was heated to 75° C. for one (1) hour. The polymer's pH wasnot adjusted. The reaction yielded 1419 g of an 8.0% solids solution ofpolyacrylamide.

To make the polyacrylic acid, 28.1 g of acrylic acid, available fromSNF, Riceboro, Ga., was added to a 1000 mL round bottom flask anddilated with 400 g of deionized water. The mixture was stirred at 275RPM and sparged with oxygen-free nitrogen for thirty (30) minutes. Afterthirty (30) minutes, the flask was heated to 45° C. and 17.80 g of a 10%V50 solution in deionized water was added to the flask. The reaction washeld at 45° C. (with a slight exotherm to 50° C.) for 45 minutes. Thepolymer's pH was not adjusted. The reaction yielded 420 g of a clear,6.9% solids solution of polyacrylic acid.

To make the poly-DADMAC, 121.4 g of DADMAC, available from SNF,Riceboro. Ga., was added to a 1000 mL round bottom flask and dilutedwith 538 g of deionized water, The mixture was stirred at 275 RPM andsparged with oxygen-free nitrogen for thirty (30) minutes. Next, thereactor was heated to 75° C. and 13.1 g of a 10% V50 solution indeionized water was added to the flask, via syringe pump, over the next120 minutes. After 120 minutes, an additional 3.3 g aliquot of 10% V50solution in deionized water was added and the temperature increased to80° C. and held for 30 minutes. The polymer's pH was not adjusted. Thereaction yielded 664 g of a clear, 12,80% solids solution ofpoly-DADMAC.

After the three polymers were made, the heterogeneous post-reactionpolymer blend was made. First, 230 g of polyacrylate (7.0 wt % solids)was slowly mixed into 380 g of the polyacrylamide solution (8.5 wt %solids). The resulting mixture was diluted with 420 g of deionized waterand stirred vigorously at 400 RPM. While the mixture was being stirred,220 g of the poly-DADMAC solution (16.6 wt % solids) was slowly added tothe blend. Any precipitated material was redissolved by stepwiseaddition of a 50% NaOH solution to adjust the pH of the blend to 7.0.

The blend results in a stable, opaque suspension of a heterogeneousblend with an active polymer concentration of 11.7 wt % and a Brookfieldviscosity of 1200 cps. The blend is 19 wt % polyacrylate, 38 wt %polyacrylamide, and 43 wt % poly-DADMAC.

Example 5 Synthesis of a Heterogeneous Polymer Blend Containing4-Slyrenestilfortic Acid Sodium Salt Hydrate (SSA), Aerviamide, andMethviacroyl-N-Propvi Trimethvl Ammonium Chloride (MAPTAC)

Samples of a SSA/acrylamide/MAPTAC heterogeneous polymer blend wereprepared by the following method. Acrylamide, available from Kemira,Kennesaw, Ga., and MAPTAC, available from Sigma Aldrich, St. Louis, Mo.,were placed in separate flasks and sparged with oxygen-free nitrogen forthirty (30) minutes.

Separately, a 500 mL 4-neck round bottom flask was equipped a condenser,a mechanical stirrer, a thermocouple attached to a regulator, a nitrogeninlet for sparging, a nitrogen outlet, and a heating mantle. 133.25 gSSA, available from Sigma Aldrich, St. Louis, Mo., and 23.72 g deionizedwater were added to the flask and stirred at 275 RPM for 30 minutes. Theflask was charged with 242 g of deionized water and stirred at 275 RPMand sparged with oxygen-free nitrogen for thirty (30) minutes.

In a separate 50 mL round bottom flask, 7.45 g of 20% solution of V50,available from Wako, Richmond, Va., was added and stirred at 275 RPMWhile sparging with oxygen-free nitrogen for thirty (30) minutes. Twentypercent (20%) (1.49 g) of the sparged V50 was added to the SSA. The 500mL flask was heated to 45° C. for 45 minutes while stirring at 275 RPM.

36.75 g of the sparged acrylamide solution was added to the 500 mLflask, followed quickly by 40% (2.98 g) of the sparged V50 solution. The500 mL flask was heated to 50° C. for 45 minutes while stirring at 275RPM. After 45 minutes, 57.06 g of the sparged MAPTAC solution and 20%(1.49 g) of the sparged V50 were added as quickly as possible. The 500mL flask was heated at 50° C. for 45 minutes while stirring at 275 RPM.

After 45 minutes, the temperature of the 500 mL flask was increased to75° C. and the remaining V50 solution (1.49 g) was added. The mixturewas heated at 75° C. for one (1) hour. The resulting solution was cooledto room temperature. The pH of the solution was measured and adjusted to7 using sodium hydroxide.

The reaction resulted in a stable, opaque suspension of a heterogeneouspolymer blend with an active polymer concentration of 15.3% and aBrookfield viscosity of 46 cps (measured using a #63 spindle, 50 RPM at22° C.). Residual SSA and acrylamide monomer was measured and found tobe less than 2 ppm. This suspension separated on dilution and requiredvigorous agitation to obtain a uniform suspension suitable for use inpapermaking.

Example 6 Synthesis of a Heterogeneous Polymer Blend Using ReverseAddition Order (As Compared to Example 1)

Samples of the heterogeneous polymer blend were prepared by thefollowing method. 161.9 g of acrylamide, available from SNF, Riceboro,Ga., and 17.76 g of acrylic acid, available from Aldrick, St. Louis,Mo., were placed in separate flasks. The acrylamide was mixed with 716.6g deionized water and 0.11 g solid Copper (II) Sulfate, available fromSigma Aldrich, St. Louis, Mo. Both flasks were sparged with oxygen-freenitrogen for thirty (30) minutes.

Separately, a 500 mL 4-neck round bottom flask was equipped with a Yconnector fitted with a 250 mL dropping funnel and a condenser, amechanical stirrer, a thermocouple attached to a regulator, a nitrogeninlet for sparging, a nitrogen outlet, and a heating mantle. 60.68 gDADMAC, available from SNF, Riceboro, Ga. were added to the flask andstirred at 275 RPM and sparged with oxygen-free nitrogen for thirty (30)minutes.

In a separate 50 mL round bottom flask, a 10% solution of V50, availablefrom Wako, Richmond, Va., was added and stirred at 275 RPM whilesparging with oxygen-free nitrogen for thirty (30) minutes. A syringepump was charged with 9.38 g of the sparged V50 solution and thesolution was injected dropwise into the 500 mL flask over 180 minutes.While the solution was being added to the flask, the temperature waskept constant at 65° C. while stirring at 275 RPM.

The sparged acrylamide solution was added to the 500 mL flask, followedquickly by 4.69 g of the sparged 10% V50 solution. The 500 mL flask wascooled to 50° C. and the temperature was maintained for one (1) hourwhile stirring at 275 RPM. After one (1) hour, 17.76 g of the acrylicacid and 4.69 g of the V50 solution were quickly added to the flask. Thetemperature was maintained at 50° C. for one (1) hour while stirring at275 RPM.

After one (1) hour, the temperature of the 500 mL flask was increased to75° C. and the remaining 4.69 g of V50 solution was added via syringepump, dropwise, over thirty (30) minutes. After the V50 solution wascompletely added, the flask was to 80° C. for one (1) hour. Theresulting solution was cooled to room temperature. The pH of thesolution was measured and adjusted to 7.4 using sodium hydroxide.

The reaction resulted in a light grey, viscous suspension of aheterogeneous polymer blend with an active polymer concentration of14.5% and a Brookfield viscosity of 20,100 cps (measured using a #63spindle, 5 RPM at 22° C.). The blend fractions were calculated usingkinetic sampling and 1H NMR sampling of the in-process composition. 1HNMR analysis showed 99.9% conversion of DADMAC into poly-DADMAC and lessthan 1 ppm unreacted acrylic acid and 253 ppm unreacted acrylamide. Theheterogeneous polymer blend did not precipitate, gel, or separate whenstored at room temperature for thirty (30) days.

Example 7 Papermaking Utility to Increase the Sheet Ash Content of theFinal Paper or Paperboard Product

The heterogeneous polymer blend of the present invention as synthesizedin Example 2 was used with clustered acicular-aragonite precipitatedcalcium carbonate filler (ULTRABULK® II PCC), available from SpecialtyMinerals, Inc., Bethlehem, Pa. The Idler had a mean particle diameter of3.9 microns. Separate runs tested the heterogeneous polymer blend of thepresent invention as a filler pre-treatment prior to papermaking and asa wet end additive during papermaking with the filler added prior to theheterogeneous polymer blend. For all runs, the polymer was added at atreatment amount equal to 0.45 wt %, based on the total dry paperfurnish. Both methods of addition resulted in superior final paperproduct properties.

The final paper product was made to a sheet ash target of 30 wt % dryweight using a pulp slurry of 70 wt % bleached hardwood and 30 wt %bleached softwood fiber. The fiber stock was refined to a freenesstarget of 450 mL CSF. Other standard additives (all expressed as wt % ofthe total dry paper furnish) included 0.75% Stalok 300 starch, availablefrom Tate and Lyle, Decatur, Ill., 0.25% alum, available from GeneralChemical, Parsippany, N.J., 0.1% Prequel 1000 ASA size, 0.015% PERFORMPC8138 flocculant, and 0.01% PERFORM SP9232 drainage aid, all availablefrom Hercules, Inc., Wilmington, Del. The size press was treated with asurface treatment of 50 lb/T of ETHYLEX 2015 hydroxyethylated cornstarch, available from Tate and Lyle, Decatur, Ill. The paper machinewas calendered to atop side smoothness target of 150 Sheffield units.

The finished paper product using the present invention was compared topaper made using the same variables and additives, but that used aclustered scalenohedral-calcite filler (SMI ALBACAR® LO PCC), availablefrom Specialty Minerals, Inc., Bethlehem, Pa., with a mean particlediameter of 2.1 microns, a 20 wt % sheet ash target, based on dry weightof the paper furnish, and no heterogeneous polymer blend. The results ofthe experiment are contained in Table 1. Use of the invention maintainedstiffness and strength as filler content increased, when compared to theALBACAR® LO PCC control at higher filler content. Both fillerpretreatment and addition of the copolymer to the pulp furnish helpedmaintain paper strength at higher filler loading.

TABLE 1 UTILITY OF THE PRESENT INVENTION AS A FILLER TREATMENT ALBACAR ®ULTRABULK ® II ULTRABULK ® ALBACAR ® Filler LO PCC PCC II PCC LO PCCChemical Treatment No Example 2-0.45% Example 2-0.45% No Applicationpoint None Wet End Filler None Ash (525C) (%) 20.9 29.8 29.5 31.0 MDTaber Stiffness (gf-cm) 2.49 2.52 2.32 2.21 CD Taber Stiffness (gf-cm)1.11 1.06 1.01 0.91 GM Taber Stiffness (gf-cm) 1.66 1.63 1.53 1.42 GMTensile (lbf/in) 12.61 12.19 10.81 9.87 ZD Tensile (psi) 75.7 71.2 72.667.1

Example 8 Comparison of the Heterogeneous Polymer Blend to a TwoComponent Polymer Blend Addition

The heterogeneous polymer blend of the present invention was synthesizedas in Example 3 and compared to a post-reaction cationic/anionic polymerblend. The cationic and anionic polymers were derived from the samecationic and anionic monomers used to synthesize the heterogeneouspolymer blend of Example 3, and are available as PERFORM PC8229 andHERCOBOND 2000, both available from Hercules, Inc., Wilmington, Del.

A final paper product was made to a sheet ash target of 30 wt % dryweight using a Pulp slurry of 70 wt % bleached hardwood and 30 wt %bleached softwood fiber. The fiber stock was refined to a freenesstarget of 450 mL CSF. Other standard additives (all expressed as wt % ofthe total dry paper furnish) included 0.75% Stalok 300 starch, availablefrom Tate and Lyle, Decatur, Ill., 0.25% alum, available from GeneralChemical, Parsippany, N.J., 0.1% Prequel 1000 ASA size, 0.015% PERFORMPC8138 flocculant, and 0.01% PERFORM SP9232 drainage aid, all availablefrom Hercules, Inc., Wilmington, Del. The size press was treated with asurface treatment of 50 lb/T of ETHYLEX 2015 hydroxyethylated cornstarch, available from Tate and Lyle, Decatur, Ill. The paper machinewas calendered to a top side smoothness target of 150 Sheffield units.Additionally, the finished paper product made using the presentinvention was compared to paper made using the same variables andadditives, but that used a clustered scalenohedral-calcite filler (SMIALBACAR® LO PCC), available from Specialty Minerals, Inc., Bethlehem,Pa., with a mean particle diameter of 2.1 microns, a 20 wt % sheet ashtarget, based on dry weight of the paper furnish, and no heterogeneouspolymer blend. The results of the run are contained in Table 2.

At a constant top smoothness of 150 Sheffield units, bath polymertreatments improved both the in-plane and z-directional tensileproperties over the untreated finished paper. The acicular-aragoniteprecipitated calcium carbonate exhibits some strength advantagescompared to the clustered scalenohedral-calcite precipitated calciumcarbonate with no polymer added. However, the heterogeneous polymercompound in conjunction with the acicular-aragonite precipitated calciumcarbonate filler provided the highest stiffness values and the overallbest finished paper qualities.

TABLE 2 COMPARISION OF BLEND PERFORMANCE V. TWO COMPONENT ADDITIONALBACAR ® ALBACAR ® ULTRABULK ® ULTRABULK ® ULTRABULK ® Filler LO PCC LOPCC II PCC II PLC II PCC Chemical Treatment No No Example 3-0.45%Perform ® No PC8229-0.036% Hercobond ® 2000-0.45% Application None NoneWet End Wet End None Ash (525C) (%) 1.9.0 28.8 28.7 27 .7 31.9 MD TaberStiffness 2.29 2.09 2.33 2.18 2.05 (gf-cm ) CD Taber Stiffness 0.85 0.790.96 0.79 0.83 (gf-cm) GM Taber Stiffness 1.39 1.29 1.50 1.32 1.30(gf-cm) GM Tensile (lbf/in) 12.51 9.07 11.06 11.08 9.45 ZD Tensile(lbf/in) 75.9 56.6 64.9 74.9 62.2

Example 9 Comparison of the Present Invention to a Post-Reaction Blend

The heterogeneous polymer blend of the present invention was synthesizedas in Example 2 and compared to a post-reaction polymer blend asprepared in Example 4.

A final paper product was made to a sheet ash target of 30 wt % dryweight using a pulp slurry of 70 wt % bleached hardwood and 30 wt %bleached softwood fiber. The fiber stock was refined to a freenesstarget of 450 mL CSF. Other standard additives (all expressed as wt % ofthe total dry paper furnish) included 0.75% Stalok 300 starch, availablefrom Tate and Lyle, Decatur, Ill., 0.25% alum, available from GeneralChemical, Parsippany, N.J., 0.1% Prequel 1000 ASA size, 0.015% PERFORMPC8138 flocculant, and 0.01% PERFORM SP9232 drainage aid, all availablefrom Hercules, Inc., Wilmington, Del. The size press was treated with asurface treatment of 50 lb/T of ETHYLEX 2015 hydroxyethylated cornstarch, available from Tate and Lyle, Decatur, Ill. The paper machinewas calendered to a top side smoothness target of 150 Sheffield units.Additionally, the finished paper product made using the presentinvention was compared to paper made using the same variables andadditives, but that used a clustered scalenohedral-calcite filler (SMIALBACAR® LO PCC), available from Specialty Minerals, Inc., Bethlehem,Pa., with a mean particle diameter of 2.1 microns, a 20 wt % sheet ashtarget, based, on dry weight of the paper furnish, and no heterogeneouspolymer blend. The results of the run are contained in Table 3.

At a constant top smoothness of 150 Sheffield units, both polymertreatments improved both the in-plane and z-directional tensileproperties over the untreated finished paper. However, the heterogeneouspolymer compound in conjunction with the acicular-aragonite precipitatedcalcium carbonate filler provided the highest stiffness values and theoverall best finished paper qualities.

TABLE 3 COMPARISON OF IN-SITU HETEROGENEOUS POLYMER BLEND TO POST-REACTION HOMOPOLYMER BLEND ALBACAR ® ULTRABULK ® ULTRABULK ® Filler LOPCC II PCC II PCC Chemical Treatment No Example 2-0.45% Example 4-0.45%In-situ blend Post-reaction blend Application Point None Wet End Wet EndAsh (525C) (%) 31.0 29.8 30.2 MD Taber Stiffness (gf-cm) 2.21 2.52 2.37CD Taber Stiffness (gf-cm) 0.91 1.06 1.01 GM Taber Stiffness (gf-cm)1.42 1.63 1.55 GM Tensile (lbf/in) 9.87 12.19 11.34 ZD Tensile (psi)67.1 71.2 66.5

Example 10 Ability of the Heterogeneous Polymer Blend to Increase orMaintain Paper Machine Runnability

The heterogeneous polymer blend was synthesized as in Example one andevaluated on a Noble and Wood handsheet study to evaluate the blend'seffect on paper machine runnability. The fiber furnish for the runsconsisted of 70 wt % of 360 mL CSF bleached hardwood Kraft blended with30 wt % 500 mL CSF bleached softwood Kraft. An inorganic calciumcarbonate filler of ULTRABULK® II PCC, available from SpecialtyMinerals, Inc., Bethlehem, Pa., was added to the fiber furnish toconsist of between 20 and 30 wt %, based on the dry weight of the paperfurnish. Additionally, a control sheet using ALBABAR® LO PCC but withoutthe heterogeneous polymer blend was made for comparison purposes. Thesuspension was diluted with 1 wt % solids, based on the dry weight ofthe paper furnish. A standard additive package of 0.75% Stalok 300starch, available from Tate and Lyle, Decatur, Ill., 0.25% alum,available from General Chemical, Parsippany, N.J., 0.02% PERFORM PC8138flocculant, and 0.02% PERFORM SP7200 drainage aid was added to thefurnish (all percentages are based on the dry weight % of the totalfurnish).

Aliquots of the treated and untreated furnish were used to produce8×8-inch square handsheets with a target basis weight of 90 lbs/3000square feet. The sheets were pressed via standard conditions but werenot dried. Each pressed sheet was then sandwiched between two plastictransparency sheets and a paper cutter was used to cut thepaper/transparency sheets into 1-inch wide strips. The strips weretested for never-dried wet tensile strength using an Instron-typemachine. Separate handsheets from identical test conditions were thendried to evaluate each test condition for solids, basis weight, andretained ash content. These evaluations were done using standard TAPPImethods.

Increasing the retained sheet ash from 17 to 25 wt %, based on the dryweight of the finished paper, in conjunction with the filler type changeresulted in a 56% drop in never-dried wet tensile strength with nochange in press solids. The addition of 0.2 wt %, based on the dryweight of the paper furnish, of the heterogeneous polymer blend fromExample 1, improved performance over the untreated furnish by 38%. Whenthe paper furnish was treated with 0.4 wt %, based on the dry weight ofthe paper furnish, it improved performance over the untreated furnish by65%.

Paper machine runnability is closely related to the cohesiveness of thewet web exiting the press section; the higher cohesiveness, the more“runnable” the furnish. The addition of the heterogeneous polymer blendof the present invention increased the web's cohesiveness, which isexpected to translate into improved paper machine runnability atelevated sheet ash content. The results of are provided in Table 4.

TABLE 4 IMPROVEMENT IN WET WEB COHESION Condition Ash Filter Wet TensileSolids Units (525C) (%) Type (lbf/in) (%) Control 16.7 ALBACAR LO ® 0.9249.9 PCC Control 25.5 ULTRABULK ® 0.40 49.7 II PCC 0.2% Example 1 25.4ULTRABULK ® 0.60 47.1 II PCC 0.4% Example 1 24.7 ULTRABULK ® 0.74 46.3II PCC

Example 11 Utility of the Heterogeneous Polymer Blends to DecreaseSlurry Abrasiveness

The heterogeneous polymer blend of the present invention was synthesizedas in Example 1 and evaluated against an untreated filler/slurrymixture, and slurry mixture treated with 1.5 wt %, based on the dryweight of the slurry, of a two componentpoly-DADNIAC/aerylate/acrylamide copolymer. Both ALBACAR® SP PCC andULTRABULK® PCC, both available from Specialty Minerals, Inc., Bethlehem,Pa., were used as the inorganic filler for evaluation.

Abrasion potential was evaluated using an Einlehner abrasion tester(model AT2000) to determine how the slurries would cause wear on thesynthetic wires of paper machines. The amount of wear caused by thefillers or other additives is determined by the weight loss of a testwire. The test wire loses material as a result of the sliding frictiongenerated by a rotary abrader “test body” in an aqueous suspension ofthe filler or pigment that is being tested. The weight the test wireloses after completion of a specific distance at a defined pressurelevel is used to compare the amount of wear caused by the filler orpigment tested.

The test wire is fed around a rotary abrader consisting of ceramicledges. The rotary abrader is attached to the bottom of the verticaldrive shaft and is open at the top. The test wire engages a fixedsupporting rod and a supporting rod that pivots around this fixed rodand is pressed against the rotary abrader by a loading weight. The testwire and the rotary abrader are immersed completely in a suspension ofthe filler or pigment that is in a glass test cylinder. The suspensionis able to reach the test wire from the inside through the gaps betweenthe ceramic ledges of the rotary abrader, with the help of the suctioncreated between the wire and the rotary abrader. The suspension is keptthoroughly mixed by the rotary movement of the ceramic ledge abrader.The suspension consistency is chosen so that the weight loss is intarget with a reference GCC filler sample with both rotary abraders. Theoutside of the wire is covered with adhesive tape, so that an adequatefilm of liquid forms between the ceramic ledges and the wire.

The standard setting for the Einlehner AT2000 abrasion test is 1-kgweight for wire tension, and 25,000 meters distance for rotary abradermovement. The rotary abrader moves at a speed of 333 m/min, so one testtakes 75-minutes to complete. The filler samples were tested once withtwo rotary abraders, and the resulting weight loss (in mg) is an averageof these two measurements. The sample amount per test was 9.5 g dry fortest body #2062, and 8.5 g dry for test body #2137.

Slurry runs were evaluated for both the ALBACAR® SP PCC and theULTRABULK® II PCC for the following: untreated slurry, 1.5 wt %, basedon the dry weight of the slurry, of the heterogeneous polymer blend, 1.5wt %, based on the dry weight of the slurry, of the two componentcompound. While use of the two component polymer only resulted in aslight decrease in slurry abrasiveness, the heterogeneous polymercompound of the present invention resulted in a remarkable decrease inslurry abrasion. The results of the various runs are summarized in Table5.

TABLE 5 SLURRY ABRASIVITY VIA EINLEHNER ABRASION ANALYSIS ALRACAR ®ULTRABULK ® SP PCC II PCC (mg weight loss) (mg weight loss) UntreatedControl 9.0 7.0 Example 1 treated 3.4 4.1 (1.5% on filler) Perform ®PC8229, 8.0 6.1 Hercobond ® 2000 treated (1.5% on filler)

Example 12 Papermaking Utility of a SSA/AM/MAPTAC Heterogenous PolymerBlend

The SSA/AM/MAPTAC heterogeneous polymer blend was synthesized as inExample 5 and added to a pulp slurry to evaluate the properties of afinal paper product made from the slurry. ALBACAR® LO PCC was used asthe inorganic filler. The heterogeneous polymer blend was mixed with theALBACAR® LO PCC and allowed to stir with low shear at room temperatureprior to addition to the slurry.

The final paper product was made as in Example 7 to a sheet ash targetof 30 wt % dry weight using a pulp slurry of 70 wt % bleached hardwoodand 30 wt % bleached softwood fiber. The fiber stock was refined to afreeness target of 450 mL CSF. Other standard additives (all expressedas wt % of the total dry paper furnish) included 0.75% Stalok 300starch, available from Tate and Lyle, Decatur, Ill., 0.25% alum,available from General Chemical, Parsippany, N.J., 0.1% Prequel 1000 ASAsize, 0.015% PERFORM PC8138 flocculant, and 0.01% PERFORM SP9232drainage aid, all available from Hercules, Inc., Wilmington, Del. Thesize press was treated with a surface treatment of 50 lb/T of ETHYLEX2015 hydroxyethylated corn starch, available from Tate and Lyle,Decatur, Ill. The paper machine was calendered to a top side smoothnesstarget of 150 Sheffield units.

Both polymeric products allowed a higher final ash content in the finalpaper product, without degradation of strength relative to the 20 wt %ash control sheet. The results of the run are contained in Table 6.

TABLE 6 COMPARISON OF SSA/AM/MAPTAC HETEROGENEOUS POLYMER BLENDPERFORMANCE TO AN AA/AM/DADMAC HETEROGENEOUS POLYMER BLEND PERFORMANCEALBACAR ® ALBACAR ® ALBACAR ® ALBACAR ® Filler LO PCC LO PCC LO PCC LOPCC Chemical Treatment No No Example 3-2% Example 5-2% relative torelative to PCC PCC solids solids Application Point None None PCC pre-PCC pre- treatment treatment Ash (525C) (%) 21.1 30.7 26.6 26.71 MDTaber Stiffness 2.13 1.79 2.37 2.38 (gf-cm) CD Taber Stiffness 0.79 0.690.72 0.76 (gf-cm) GM Taber Stiffness 1.30 1.11 1.31 1.35 (gf-cm) GMTensile (lbf/in) 12.18 10.29 11.43 11.89 ZD Tensile (psi) 99.0 72.4 90.092.6

Example 13 Comparison of the Heterogeneous Polymer Blend with aHeterogeneous Polymer Blend Synthesized by Reversing Addition Order

The heterogeneous polymer blend as synthesized in Example 3 was comparedagainst the heterogeneous polymer blend synthesized by reversing theaddition or, as in Example 6 and the efficacy of the two polymer blendswas compared. ULTRABULK® II PCC was used as the inorganic filler.Additionally, an untreated ALBACAR® LO PCC control sheet was formed.

The final paper product was made as in Example 7 to a sheet ash targetof 30 wt % dry weight using a pulp slurry of 70 wt % bleached hardwoodand 30 wt % bleached softwood fiber. The fiber stock was refined to afreeness target of 450 mL CSF. Other standard additives (all expressedas wt % of the total dry paper furnish) included 0.75% Stalok 300starch, available from Tate and Lyle, Decatur, Ill., 0.25% alum,available from General Chemical, Parsippany, N.J., 0.1% Prequel 1000 ASAsize, 0.015% PERFORM PC8138 flocculant, and 0.01% PERFORM SP9232drainage aid, all available from Hercules, Inc., Wilmington, Del. Thesize press was treated with a surface treatment of 50 lb/T of ETHYLEX2015 hydroxyethylated corn starch, available from Tate and Lyle,Decatur, Ill. The paper machine was calendered to atop side smoothnesstarget of 150 Sheffield units.

At a constant smoothness of 150 Sheffield units, the heterogeneouspolymer blend as synthesized in Example 3 performed better than theheterogeneous polymer blend synthesized using the reverse additionorder. Both blends performed better than the untreated control. Theresults are summarized in Table 7.

TABLE 7 PERFORMANCE COMPARISON OF HETEROGENEOUS POLYMER BLENDS MADE INREVERSE REACTION ORDER Filler ALBACAR ® ALBACAR ® ULTRABULK ®ULTRABULK ® LO PCC LO PCC II PCC II PCC Chemical Treatment No No Example6 0.45% Example 3 0.45% Application Point None None Wet End Wet End Ash(525C) (%) 20.0 28.9 29.5 29.1 MD Taber Stiffness 2.39 1.92 1.94 1.90(gf-cm) CD Taber Stiffness 1.03 0.81 0.85 0.88 (gf-cm) GM TaberStiffness 1.56 1.25 1.28 1.29 (gf-cm) GM Tensile (lbf/in) 11.64 8.929.60 10.39 ZD Tensile (psi) 80.8 67.9 75.7 85.0

Example 14 Papermaking Utility as a Comparison of ALBACAR® SP-3 andULTRABULK® II Precipitated Calcium Carbonates Used with theHeterogeneous Polymer Blend

The heterogeneous polymer blend of the present invention was synthesizedas in Example 6 and the properties of a final paper product wereevaluated using two different precipitated calcium carbonate fillers—aacicular-aragonite precipitated calcium carbonate (ULTRABULK® II PCC)and a clustered scalenohedral precipitated calcium carbonate (ALBACAR®SP-3), both available from Specialty Minerals, Inc., Bethlehem, Pa.,Wilmington, Del. The two fillers had mean particle diameters of 3.9 and3.0 microns, respectively. Paper made from pulp slurry containing onlythe inorganic filler was used as a control.

The final paper product was made as in Example 7 to a sheet ash targetof 30 wt % dry weight using a pulp slurry of 70 wt % bleached hardwoodand 30 wt % bleached softwood fiber. The fiber stock was refined to afreeness target of 450 mL CSF. Other standard additives (all expressedas wt % of the total dry paper furnish) included 0.75% Stalok 300starch, available from Tate and Lyle, Decatur, Ill., 0.25% alum,available from General Chemical, Parsippany, N.J., 0.1% Prequel 1000 ASAsize, 0.015% PERFORM PC8138 flocculant, and 0.01% PERFORM SP9232drainage aid, all available from Hercules, Inc., Wilmington, Del. Thesize press was treated with a surface treatment of 50 lb/T of ETHYLEX2015 hydroxyethylated corn starch, available from Tate and Lyle,Decatur, Ill. The paper machine was calendered to a top side smoothnesstarget of 150 Sheffield units. The results of the run are contained inTable 8 (ALBACAR® and Table 9 (ULTRABULK®).

At a constant top smoothness of 150 Sheffield units, final paper madefrom pulp slurry containing the ULTRABULK® PCC or ALBACAR SP-3 PCCtreated with the heterogeneous polymer mixture performed better thanuntreated paper.

TABLE 8 PERFORMANCE COMPARISON OF THE HETEROGENEOUS POLYMER BLEND WITHALBACAR ® SP-3, AND UNTREATED FINISHED PAPER ALBACAR ® ALBACAR ®ALBACAR ® ALBACAR ® ALBACAR ® Filler LO PCC LO PCC SP-3 PCC SP-3 PCCSP-3 PCC Chemical No No No Example 3 Example 3 Treatment 0.33% 0.50%Application None None None Wet End Wet End Point Ash (525C) 21.0 29.630.4 29.1 30.1 (%) MD Taber 1.99 1.60 1.54 1.65 1.68 Stiffness (gf-cm)CD Taber 0.81 0.58 0.65 0.67 0.71 Stiffness (gf-cm) GM Taber 1.27 0.971.00 1.05 1.09 Stiffness (gf-cm) GM Tensile 9.24 7.26 7.27 7.89 8.02(lbf/in) ZD Tensile 73.2 61.1 63.0 69.6 69.2 (psi)

TABLE 9 PERFORMANCE COMPARISON OF THE HETEROGENEOUS POLYMER BLEND WITHULTRABULK ® II, AND UNTREATED FINISHED PAPER ULTRABULK ® ULTRABULK ®ULTRABULK ® Filler II PCC II PCC II PCC Chemical Treatment No Example 30.33% Example 3 0.50% Application Point None Wet End Wet End Ash (525C)(%) 31.0 29.5 28.7 MD Taber Stiffness (gf-cm) 1.69 1.67 1.70 CD TaberStiffness (gf-cm) 0.61 0.76 0.79 GM Taber Stiffness (gf-cm) 1.02 1.131.16 GM Tensile (lbf/in) 8.02 8.50 8.72 ZD Tensile (psi) 69.6 68.6 72.8

It will be appreciated by those skilled in the art that changes could bemade to the embodiments and examples described above without departingfrom the broad inventive concept thereof. It is understood, therefore,that this invention is not limited to the particular embodiments andexamples disclosed, but is instead intended to cover modificationswithin the spirit and scope of the present invention as defined by theappended claims.

What is claimed is:
 1. A method of making a heterogeneous polymer blend,comprising: a. adding to a non-neutral solution a first amount of apolymerization initiator and one or more anionic or cationic monomers,wherein each monomer has the same charge; b. adding a second amount ofthe polymerization initiator and one or more non-ionic monomers to thesolution; c. adding a third amount of the polymerization initiator andone or more ionic monomers that are oppositely charged from the monomersof (a); d. adding stepwise, a fourth amount of the polymerizationinitiator to react any residual monomer and resulting in theheterogeneous polymer blend; and e. neutralizing, if necessary, theresulting heterogeneous polymer blend.
 2. The method of claim 1 wherein(a) the anionic monomer(s) are selected from the group consisting of:(1) acrylic acid, (2) methacrylic acid, (3) styrenesulfonic acid, (4)vinylsulfonic acid, (5) acrylamidomethylpropane sulfonic acid, and (6)mixtures thereof; (b) the cationic monomer(s) are selected from thegroup consisting of: (1) diallyldimethylammonium chloride, (2)acryloylethyltrimethyl ammonium chloride, (3) methacryloylethyltrimethyl ammonium chloride, (4) acryloylethyltrimethylammonium sulfate,(5) methacryloylethyl trimethyl ammonium sulfate, (6)acrylamidopropyltrimethyl ammonium chloride, (7) methacrylamidopropyltrimethyl ammonium chloride, (8) non-quaternized forms of (2)-(7), (9)vinylformamide (subsequently hydrolyzed to vinylamine), and (10)mixtures thereof; and (c) the nonionic monomer(s) are selected from thegroup consisting of: (1) acrylamide, (2) methacrylamide, (3)N-alkylacrylamide, (4) vinylformamide, and (5) mixtures thereof.
 3. Themethod of claim 1 wherein the polymerization initiator is a watersoluble azo initiator.
 4. The method of claim 1 wherein the solutioncontains from about 10 mol % to about 30 mol % anionic monomer(s), fromabout 40 mol % to about 80 mol % non-ionic monomer(s), and from about 10mol % to about 30 mol % cationic monomer(s).
 5. The method of claim 2wherein the anionic monomer comprises acrylic acid, wherein the cationicmonomer comprises at least one of diallyldimethylammonium chloride oracrylamidopropyltrimethyl ammonium chloride and wherein the nonionicmonomer of comprises acrylamide.
 6. The method of claim 2 wherein theanionic monomer comprises styrenesulfonic acid oracrylamidomethylpropane sulfonic acid, wherein the cationic monomercomprises at least one of acryloylethyltrimethyl ammonium chloride ornon-quaternized form of acryloylethyltrimethyl ammonium chloride, orvinylformamide (subsequently hydrolyzed to vinylamine), and wherein thenonionic monomer comprises vinylformamide.
 7. A heterogeneous polymerblend, comprising: a. one or more anionic polymers formed from at leastone anionic monomer selected from the group consisting of: (1) acrylicacid, (2) methacrylic acid, (3) styrenesulfonic acid, (4) vinylsulfonicacid, (5) acrylamidomethylpropane sulfonic acid, and (6) mixturesthereof; b. one or more cationic polymers formed from at least onecationic monomer selected from the group consisting of: (1)diallyldimethylammonium chloride , (2) acryloylethyltrimethyl ammoniumchloride (3) methacryloylethyl trimethyl ammonium chloride, (4)acryloylethyltrimethylammonium sulfate (5) methacryloylethyl trimethylammonium sulfate, (6) acrylamidopropyltrimethyl ammonium chloride, (7)methacrylamidopropyl trimethyl ammonium chloride, (8) non-quaternizedforms of (2)-(7), (9) vinylformamide (subsequently hydrolyzed tovinylamine), and (10) mixtures thereof; c. one or more non-ionicpolymers formed from at least one nonionic monomer selected from thegroup consisting of: (1) acrylamide, (2) methacrylamide, (3)N-alkylacrylamide, (4) vinylformamide, and (5) mixtures thereof, andwherein the molar ratio of monomer used to make the homogeneous polymerblend is in the range of from about 10 to about 30 mol % anionicmonomer, from about 40 to about 80 mol % nonionic monomer, and fromabout 10 to about 30 mol % cationic monomer.
 8. The heterogeneouspolymer blend of claim 7, further comprising: (d) one or more copolymerscomprising at least one anionic monomer and at least one non-ionicmonomer, and (e) one or more copolymers comprising at least one cationicmonomer and at least one non-ionic monomer.
 9. The heterogeneous polymerblend of claim 8, further comprising: (f) one or more terpolymerscomprising at least one anionic monomer, at least one cationic monomer,and at least one non-ionic monomer.
 10. The heterogeneous polymer blendof claim 7 wherein the anionic monomer of a. comprises acrylic acid,wherein the cationic monomer of b. comprises at least one ofdiallyldimethylammonium chloride or acrylamidopropyltrimethyl ammoniumchloride and wherein the nonionic monomer of c. comprises acrylamide.11. The heterogeneous polymer blend of claim 7 wherein the anionicmonomer of a. comprises styrenesulfonic acid or acrylamidomethylpropanesulfonic acid, wherein the cationic monomer of b. comprises at least oneof acryloylethyltrimethyl ammonium chloride or non-quaternized form ofacryloylethyltrimethyl ammonium chloride, or vinylformamide(subsequently hydrolyzed to vinylamine), and wherein the nonionicmonomer of c. comprises vinylformamide.
 12. A heterogeneous polymerblend, comprising: a. one or more anionic polymers formed from at leastone anionic monomer selected from the group consisting of: (1) acrylicacid, (2) methacrylic acid, (3) styrenesulfonic acid, (4) vinylsulfonicacid, (5) acrylamidomethylpropane sulfonic acid, and (6) mixturesthereof; b. one or more cationic polymers formed from at least onecationic monomer selected from the group consisting of: (1)diallyldimethylammonium chloride , (2) acryloylethyltrimethyl ammoniumchloride (3) methacryloylethyl trimethyl ammonium chloride, (4)acryloylethyltrimethylammonium sulfate (5) methacryloylethyl trimethylammonium sulfate, (6) acrylamidopropyltrimethyl ammonium chloride, (7)methacrylamidopropyl trimethyl ammonium chloride, (8) non-quaternizedforms of (2)-(7), (9) vinylformamide (subsequently hydrolyzed tovinylamine), and (10) mixtures thereof; c. one or more non-ionicpolymers formed from at least one nonionic monomer selected from thegroup consisting of: (1) acrylamide, (2) methacrylamide, (3)N-alkylacrylarnide, (4) vinylformamide, and (5) mixtures thereof;wherein the active polymer concentration of the heterogeneous polymerblend is 10% or greater.
 13. The heterogeneous polymer blend of claim 12wherein the anionic monomer of a. comprises acrylic acid, wherein thecationic monomer of b. comprises at least one of diallyldimethylammoniumchloride or acrylamidopropyltrimethyl ammonium chloride and wherein thenonionic monomer of c. comprises acrylamide.
 14. The heterogeneouspolymer blend of claim 12 wherein the anionic monomer of a. comprisesstyrenesulfonic acid or acrylamidomethylpropane sulfonic acid, whereinthe cationic monomer of b. comprises at least one ofacryloylethyltrimethyl ammonium chloride or non-quaternized form ofacryloylethyltrimethyl ammonium chloride, or vinylformamide(subsequently hydrolyzed to vinylamine), and wherein the nonionicmonomer of c. comprises vinylformamide.